This invention relates to an improved wave antenna scanner for a radar apparatus and, more particularly, to a compact design that is formed with a minimum number of components.
The present construction is directed towards a motor vehicular collision warning system which includes a scanned beam sensor, a signal processor, and a vehicle interface system that initiates warnings to the driver or adaptively controls the vehicle. In this forward looking collision warning system, the sensor is designed to project a narrow beam of energy toward objects in the forward field of view. A forward collision warning control of this type for a vehicle can require a unit life in excess of two hundred million cycles at temperatures ranging from xe2x88x9240xc2x0 to 100xc2x0 C. Thus, reliability requirements are high and unit costs must be low.
Conventional radar apparatus have included wave guide antenna for transmission and reception of radar signals. A conventional rotary drive is commonly used to rotate the antenna scanner. Since known wave antenna scanners use electric motors, they must be brushless to operate for the number of cycles to meet life rating specifications. These electric motors are, therefore, expensive and require a complex commutation scheme and sophisticated control electronics. Further, the electronic noise produced by switching and commutation can adversely affect the sensor and signal processing for the radar apparatus.
Another problem inherent with existing motors for use with wave antenna scanners relates to the gear reducer that is often required to provide slow speed operation. Scanning mechanisms which are composed of motors and bearings with gears or the like are inherently short lived due to the large number of moving parts and the need for lubrication. There are also problems associated with noise as a result of the wear on the parts after repeated cycling. Finally, conventional electric motors add waste heat within the system package that exacerbates the problem of cooling the sealed electronic package near the engine of the automobile.
Therefore, it is an object of the present invention to avoid the aforementioned disadvantages and problems associated with existing wave antenna scanners.
In accordance with this invention, a radar apparatus is provided with a rotatable antenna structure such as a slotted wave guide antenna. The antenna is driven to oscillate back and forth at an angle of 12xc2x0 or less in each direction. A transceiver is coupled to the antenna and the antenna passes transmitted and reflected radar signals to and from a target as it is oscillated back and forth. The scanned signals are directed to a processor and then to a vehicle interface system for initiating warnings to the driver or adaptively controlling the vehicle.
The rotatable antenna is mounted to a tuned mass and spring scanner assembly which is designed to produce a controlled harmonic oscillation at a specific resonance frequency when excited by a chain of timed electrical impulses. The impulse timing, duration and amplitude are based upon feedback provided by a position sensor on the scanner.
The scanner is an electromechanical mechanism consisting of a moving support with one end mounted by way of a spring flexure device to a stationary chassis and the other end mounting the scanning antenna. The drive for the moving support is magnetic and has no contacting components. The moving support is connected to the stationary chassis by the spring flexure device. The moving support and spring assembly use the spring as an energy reservoir thereby taking advantage of its natural resonance for providing a tuned mechanism. A coil and magnet drive the moving support such that there is no electrical wiring or signals transferred from the moving support to the stationary chassis. Further, there are no bearings and no sliding or fretting thereby preventing any Coulomb friction. Moreover, the assembly is shock tolerant since the spring flexure device has a high axial spring rate to provide robustness and a controlled radial spring rate for providing harmonic oscillation.
The scanner position sensor is used for closed loop control to maintain the proper scan angle and also provide position information to the signal processor. Electronic control is provided by a microprocessor. The resonant nature of the scanner drive allows low power consumption. The resulting assembly is capable of predictable and efficient oscillatory motion. Further, since the assembly is unencumbered by friction, its life is controlled by the durability of the drive electronics and the fatigue characteristics of the spring device.